I got older. As I got older, I got more empathy - maybe partly just from getting older, but partly also by working on myself. I prayed and meditated a lot, trying to figure out why I was chasing the things I was chasing. The ego boost of being a jerk is one of those things I was sometimes chasing. Why? What was I really looking for there?
I also got married. And then I had kids. I got to see, up close and in my face, the damage that being a jerk did to other people - people I cared about, people that I either had to just continue to look at the damage or try to pick up the pieces. Seeing the hurt on peoples' faces quickly took the fun out of being a jerk.